Protective means for circuit interrupting devices



July 12, 1966 L. DENAULT 3,

PROTECTIVE MEANS iok CIRCUIT INTERRUPTINEE DEVICES Filed Aug. 11, 1964 FIG. 3B.

WITNESSES: INVENTOR Chnron L. Denoult i? W BY fi' W fia? United States Patent 3,260,894 PROTECTIVE MEANS FOR CIRCUIT INTERRUPTING DEVICES Clinton L. Denault, Hickory Township, Sharpsville County, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 11, 1964, Ser. No. 388,846 6 Claims. (Cl. 317-11) This invention relates in general to electric circuit interrupting devices and more particularly to protective apparatus f-or circuit interrupting devices.

Circuit interrupting devices, such as circuit breakers, contactors, and under-load tap changers are all subject to arcing and its deleterious effects on contact life and the insulating dielectric. Because of the arcing problem present when interrupting the flow of electrical current to a load, and also due to contact bounce upon closing an electrical circuit with mechanical contacts, expensive contact structures are utilized, which still require costly maintenance and out ofservice periods. Further, if an insulating dielectric is used in the circuit interrupter, arcing causes its electrical insulating qualities to deteriorate because the high temperature of the arc causes the dielectric to break down into undesirable products. Also, the arcing may allow several cycles of current to flow before the arc can be extinguished, which is undesirable in many applications which require a fast sequence of switching operations, such as under-load tap changers. It would, therefore, be desirable to interrupt the load current in an electrical circuit at the first current zero after the circuit interrupting device has opened the circuit, and it would be desirable to interrupt the load current and close the electrical circuit with substantially no arcing.

Accordingly, it is an object of this invention to provide new and improved circuit interrupting apparatus.

Another object of this invention is to provide new and improved protective apparatus for circuit interrupting devices which substantially eliminate arcing when load current is interrupted.

A further object of this invention is to provide new and improved protective apparatus for circuit interrupting devices which substantially eliminate arcing when closing an electrical circuit.

Another object of the invention is to provide new and improved protective apparatus for circuit interrupting devices which interrupts load current at the first current zero after the circuit interrupting device breaks the electrical circuit, with substantially no arcing.

Briefly, the present invention accomplishes the above cited objects by connecting a protective circuit in parallel with a set of auxiliary contacts on the circuit interrupting device, with the auxiliary contacts being arranged to open after the main contacts open and .to close before the main contacts close. Since conventional arcing contacts, which are connected in parallel with the main contacts, operate in exactly this manner, the conventional arcing contacts may be used if desired. The auxiliary contacts are connected in series circuit relation with the primary winding of a control transformer, which has two secondary windings, each connected in circuit relation with the gate or control electrode of separate controlled rectifiers, such as semiconductor silicon controlled rectifiers. The controlled rectifiers are connected in circuit relation with the load circuit, with one controlled rectifier poled to carry the positive cycle of the load current when it is in its conducting mode, and the other controlled rectifier poled to carry the negative cycle of the load current when it is in its conducting mode. Thus, when the main contacts of the circuit interrupting device open, the load current is carried by the auxiliary contacts until they open.

When the auxiliary contacts momentarily carry the load current, the control transformer is energized and a positive current pulse is applied to the gate electrode of the proper controlled rectifier, depending upon whether the interruption of the load current occurred during the positive or negative cycle. Thus, the proper controlled rectifier becomes conductive and carries the load current when the auxiliary contacts open. The load current is carried by the controlled rectifier, however, only until the first current zero, as the controlled rectifier regains its blocking capability when the current drops to a value near zero, and since the auxiliary contacts have opened, there is no gate signal to switch the controlled rectifier back to its conductive mode. Therefore, the circuit has been interrupted at the first current zero after the auxiliary contacts open, with substantially no arcing, as at the time the main contacts opened they were shunted by the auxiliary contacts, and at the time the auxiliary contacts opened, they were shunted by the controlled rectifier protective circuit.

When the load circuit is closed, the auxiliary contacts close first, energizing the control transformer and switching one of the controlled rectifiers to its conductive mode. The controlled rectifiers carry the load current until the first current zero after the main contacts close, as the current through the auxiliary contacts after the main contacts close is insufficient to provide gate signals of sufiicient magnitude to fire the controlled rectifiers. If desired, the auxiliary contact arrangement may be such that after the main contacts close the auxiliary contacts open. This would prevent the continuous low level excitation of the gate junction which would be present if the auxiliary contacts remain closed after the main contacts close.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 shows a schematic diagram of one embodiment of the invention,

FIG. 2 shows a typical circuit interrupting arrangement .that may be used, and

FIGS. 3A and 3B show another circuit interrupting arrangement that may be used.

Referring now to the drawings and FIG. 1 in particular, there is shown a source of alternating potential 10 having output terminals 12 and 14 connected in circuit relation with a load circuit 16 through a circuit interrupting device 18, such as a circuit breaker. Terminal 12 of source potential 10 is connected to one side of circuit interrupter 18 through electrical conductor 20, terminal 14 of source potential 10 is connected to terminal 22 of load circuit 16 through electrical conductor 24, and terminal 26 of load circuit 16 is connected to the remaining side of circuit interrupter 18 through electrical conductor 28. The circuit interrupter 18 has main contacts 30 and auxiliary contacts 32, with the main contacts 30 being arranged to open before the auxiliary contacts 32 open, and to close after the auxiliary contacts 32 close. This is the same contact arrangement employed when parallel arcing contacts are utilized in a circuit interrupting device. It is not necessary, however, for the auxiliary contacts 32 to be constructed of highly arc resistant material. Both the main and auxiliary contacts, 30 and 32 respectively, may be designed solely from the standpoint of current carrying ability, with no sacrifice being required because of arcing considerations. Typical main contact-auxiliary contact arrangements that may be used are shown in FIGS. 2 and 3, with like reference numerals referring to like components in the various figures.

The sequencing by the contacts is provided in FIG. 2 by a mechanical lost time arrangement. The operating rod 41 may be electrically operated from source potential 10, as shown, or operated in any other suitable manner, with tension spring 43 tending to hold the movable contact assembly 39 in the open position. When the close push button 47 is actuated, electric solenoid 49 is energized and it overcomes the tension of spring 43 and closes the contacts 30 and 32. A latching projection 51 on operating rod 41 catches the spring loaded tripping means 53, with compression spring 55 holding tripping means 53 in contact with latching projection 51. When the trip push button 57 is actuated, a solenoid 59 is energized which overcomes the compression of spring 55 to allow spring 43 to pull the movable contact structure 39 into the open position. Upon tripping, spring 61 keeps auxiliary contacts 32 together for a short period of time, even though the main contacts 30 have opened, until the movable contact structure 39 strikes the projecting portion 63 attached to the movable portion of auxiliary contacts 32. The auxiliary contacts 32 are then parted. Upon closing, the spring 61 forces the auxiliary contacts 32 to close before the main contacts 30 are engaged.

Referring again to FIG. 1, instead of the auxiliary contacts 32 directly paralleling the main contacts 30, as in typical main and arcing contact arrangements, the auxiliary contacts are connected in circuit relation with a control transformer 34, which has a primary winding 36 and secondary windings 38 and 40 disposed in inductive relation with a magnetic core 42. The auxiliary contacts 32 are connected to primary winding 36 through electrical conductor 44, and primary winding 36 is connected to conductor 28 through electrical conductor 46.

Thus, when circuit interrupter 18 is in its closed position, substantially all of the load current will flow through main contacts 30, with the electrical circuit starting at terminal 12 of source potential 10, through electrical conductor 20 to circuit interrupter 18, through main contacts 30, through electrical conductor 28 to terminal 26 of load circuit 16, and from terminal 22 of load circuit 16 through electrical conductor 24 to terminal 14 of source potential 10. Very little load current will flow through auxiliary contacts 32 because the auxiliary contacts 32 are smaller and have a higher resistance, and the inductive reactance of the auxiliary contact circuit is higher.

When the circuit interrupter 18 is tripped or opened, the contact arrangement is such, as shown in FIG. 1, that a very slight time delay is introduced between the opening of the main contacts 30 and the auxiliary contacts 32, with the main contacts opening first. The load current is thus transferred to the circuit including the auxiliary contacts 32, with the load current flowing through conductor 20, the auxiliary contacts 32, through conductor 44 to primary winding 36 of control transformer 34, and from primary winding 36 to conductor 28 at junction 45 through conductor 46. Since the load current has not been interrupted during this transition from the main contacts 30 to the auxiliary contacts 32, there is substantially no arcing produced at the main contacts.

In order to prevent arcing at the auxiliary contacts 32 when they open, a circuit is provided in parallel with the auxiliary contacts 32. Actually, two circuits are provided to parallel or shunt the auxiliary contacts 32, one circuit for the load current when it is interrupted during a positive half cycle, and another circuit for the load current when it is interrupted during a negative half cycle. One circuit joins electrical conductor 46 at junction 48, and includes electrical conductor 50, controlled rectifier 52 and electrical conductor 54, which rejoins electrical conductor 20 at junction 56. The other circuit starts at junction 56 and includes electrical conductor 54, electrical conductor 60, which leaves electrical conductor 54 at junction 58, controlled rectifier 62, conductor 90 to junction 99, conductor 64 to junction 66, and conductor 50 to junction 48.

Thus, assume that auxiliary contacts 32 opened during the positive half cycle of load current, and assume that the positive half cycle of load current flows through load 16 from terminal 22 to terminal 26. When circuit interrupter 18 is tripped, main contacts 30 open first, transferring the load current to the auxiliary contacts 32. Then, the auxiliary contacts 32 open. The load current would flow from terminal 26 of load 16 to junction 45, through conductor 46 to junction 48, through conductor 50 to controlled rectifier 52, through controlled rectifier 52, assuming it to be in its conducting mode, which will be hereinafter described, through conductor 54 to junction 56, through conductor 2t] to terminal 12 of source 10, and from terminal 14 to source 10 through conductor 24 to terminal 22 of load 16.

If the load current is interrupted in its negative half cycle, the load current will flow from the terminal 22 of load circuit 16 to terminal 14 of source 10, from terminal 12 of source 10 to conductor 20, conductor 20 to junction 56, conductor 54 to junction 58, conductor 60 to controlled rectifier 62, through controlled rectifier 62, assuming it to be in its conducting mode, which will be hereinafter described, from controlled rectifier 62 to conductor 64, conductor 64 to junction 66, conductor 56 to junction 48, conductor 46 to junction 45, and through conductor 28 to terminal 26 of load circuit 16.

Since a parallel path for the load circuit exists around auxiliary contacts 32, there will be substantially no arcing produced at the auxiliary contacts when they open.

In the discussion of the parallel circuits around the auxiliary contacts 32, it was assumed that the controlled rectifier in the parallel circuit being used was in its conducting mode. Controlled rectifiers 52 and 62, which may be silicon controlled rectifiers, each have main electrodes, such as an anode electrode a, and a cathode electrode c, and a gate or control electrode g. Silicon controlled rectifiers have conduction characteristics similar to a thyratron. In the reverse or nonconducting direction, they exhibit the very low leakage characteristic of a silicon rectifier. In the forward or conducting direction, conduction below rated blocking voltage may be initiated by the application of a positive control pulse to the gate electrode. With the application of a positive control pulse to the gate electrode, the device switches rapidly to a conducting mode, with very low voltage drop and high current carrying capability. Once conduction has been initiated, the gate electrode no longer has control. In order to switch the device back to its blocking mode, the anode-cathode current must be reduced below a sma l value of current called the holding current. Thus, when an alternating potential is applied to a silicon controlled rectifier and a gate signal is applied to and removed from the gate electrode, current will fiow if the anode is more positive than the cathode until the end of the half cycle. At current reversal, the current from the anode to the cathode necessarily drops to zero, returning the silicon controlled rectifier to its blocking mode.

Thus, if a gate signal is momentarily applied to the gate electrode of the proper controlled rectifier during the short period of time that the load current is flowing through the auxiliary contacts 32, the proper parallel circuit around the auxiliary contacts 32 will be established, which will continue to carry the load current after the auxiliary contacts open. Further, if no further gate signals are applied to the gate electrode g after the auxiliary contacts open, the current will continue to flow in. the parallel circuit only until the first current zero.

The development of control signals and the application of the control signals to switch the desired controlled rectifier to its conductive mode is accomplished by the control transformer 34, which, as hereinbefore described, has its primary winding 36 connected in series circuit relation with auxiliary contacts 32. When circuit interrupter 18 is tripped and main contacts 36 open, the load current flows through auxiliary contacts 32 and the pri mary winding 36 of transformer 34. A voltage is induced in secondary windings 38 and 40, with their polarity dependent upon Whether the load current is in its positive or negative half cycle. If the load current is flowing into the polarity mark of primary winding 36, the positive ends of secondary windings 38 and 40 will be as shown. If load current is flowing into the opposite end of primary winding 36 from the polarity mark, the positive ends of secondary windings 38 and 40 will be reversed.

Secondary winding 38 is connected across the'gate and cathode electrodes of controlled rectifier 52, with one end of secondary winding 38 being connected through conductor 70 to conductor 54 at junction 72. The other end of secondary winding 38 is connected to gate electrode g of controlled rectifier 52 through conductor 74 and gate protecting resistor '76. A surge by-pass capacitor '78 is connected from the cathode electrode 0 to the gate electrode g of controlled rectifier 52.

The control transformer 34 should be designed such that adequate voltage will be developed in the secondary windings 38 and 40 to fire the control-led rectifiers at any time when the load current is in its protected range. Since adequate firing voltages will be produced in the secondary windings 38 and 40 by the smallest protected load current, some means is required to protect the gate electrode g from excessive firing voltages at higher load currents. This may be accomplished by voltage clipping means 80 connected across the output of one of the secondary windings, such as a Zener type diode, or, as shown, by a plurality of rectifiers such as silicon diodes. The voltage applied to the gate-cathode junction will then be limited to the sum of the threshold voltages of the silicon diodes connected in series. Silicon diodes 82 and 84 will protect against oveivoltage when the end of secondary winding 38 marked with the polarity dot is positive, and silicon diodes 86 and 88 will protect against overvoltages when the opposite end of secondary winding 38 is positive. Since the control transformer is essentially a current transformer, the voltage clipping means 80 across secondary winding 38 will also limit the voltage produced in secondary winding 40.

Secondary winding 40 is connected across the gate cathode junction of controlled rectifier 62, with one end of secondary winding 40 being connected to the anode electrode a through electrical conductor 90, and the other end being connected to the gate electrode g through electrical conductor 2 and gate protecting resistor 94. A surge by-pa-ss capacitor 96 is connected across the gatecathode junction to protect the junction from surge voltages.

In operation, assume that the circuit interrupter 18 has been tripped, and the main contacts 36" have opened. The load current will then transfer to the auxiliary contacts 32, through primary winding 36 of control transformer 34. Also, assume that the load current is in its positive half cycle, flowing into the polarity mark on primary winding 36. Thus, a positive pulse of current will be applied to the gate electrode g of controlled rectifier 52, turning it on and allowing load current to flow therethrough. Sec ondary winding 40 applies a negative pulse of current to gate electrode g of controlled rectifier 62, thus controlled rectifier 62 will remain in its nonconducting mode. When auxiliary contacts 32 open, the parallel path for load current through controlled rectifier 52 has already been established with all of the load current flowing through the controlled rectifier in the parallel pat-h hereinbefore described. The load current continues to flow in controlled rectifier 52 until the end of the current half cycle, and then it switches to its nonconductive mode, as the current has fallen below the holding value and auxiliary contacts 32 have opened and cannot provide a signal for the gate electrode g of controlled rectifier 52. The load current, therefore, stops at the first current zero after the opening of the auxiliary contacts.

If the load current was in its negative half cycle when the main contacts 30 opened, the polarity of the secondary windings would be opposite to those shown in FIG. 1, with the negative pulse being applied to controlled rectifier 5 2 and the positive pulse being applied to controlled rectifier 62, switching controlled rectifier 62 to its conducting mode. Controlled rectifier 62 would carry the load current until the first current zero after the opening of the auxiliary contacts.

Since a gate signal is applied continuously during the period of time that the auxiliary contacts are closed after the main contacts open, if the load current is in one half cycle at the time the load current is transferred to the auxiliary contacts 32 and in the opposite half cycle at the time of the opening of the auxiliary contacts, the proper controlled rectifier will be in its conducting mode, as the controlled rectifier that will be conducting is determined by the polarity of the load current at the instant the auxiliary contacts open. If the auxiliary contacts should happen to open at a current zero, the controlled rectifiers would not establish a loop in parallel with the auxiliary contacts, but none would be required as there would be no arcing of the auxiliary contacts upon their parting at a current zero.

Upon closing of circuit interrupter 18, the auxiliary contacts close first, thus immediately providing a gate signal and parallel path for the load current through the appropriate controlled rectifier. When the main contacts close, the load current will fiow through the main contacts 30, and since gate signals will cease, the current through whichever controlled rectifier is conducting will cease at the first current zero. The immediate establishment of a parallel path through a controlled rectifier upon closing circuit interrupter 18 substantially eliminates arcing due to the bouncing of contacts.

In some instances, it may not be desirable to allow continuous low level excitation of the control electrodes g of the controlled rectifiers 52 and 62 after the main contacts 3% close and circuit interrupting device 18 is in its conductive position. FIGS. 3A and 3B show a main contacta-uxiliary contact arrangement that may be used in which the auxiliary contacts 32 open after the main contacts have closed.

More specifically, FIGS. 3A and 3B show an elevation and top views, respectively, of a disconnect type switch 100 in its closed position. It will be noted that in the completely closed position, the movable portion of the auxiliary contacts 32 is not in contact with the stationary portion, thus preventing the low level excitation of the control electrodes g of the controlled rectifiers 52 and 62. Spring biasing means 61 gives positive closing and delayed spring accelerated opening of auxiliary contacts 32. Insulating operating rod 41 may be manually or automatically operated.

In selecting or designing control transformer 34, the transformer core size and number of turns of each secondary winding are determined by the smallest load current for which protection is desired. Also, the transformer should be designed such that the maximum core induction at maximum expected load current will still provide adequate voltage in the secondary windings 38 and 40 to switch the appropriate controlled rectifier to its conducting state. In determining the protective rating of a controlled rectifier, the half cycle surge current rating may be used, unless the circuit interrupter being protected is particularly sluggish. If it is desired to extend the voltage or current rating of the protective system beyond that provided by a pair of single controlled rectifiers, use may be made of well known methods of arranging the controlled rectifiers in series or parallel, or both, providing additional control windings for each added controlled rectifier.

While one control transformer 34 has been shown, it will be understood that separate control transformers may be utilized for each controlled rectifier. However, in

utilizing separate control transformers, each will have to have voltage clipping means for limiting the gate voltage.

Thus, there has been disclosed new and improved circuit interrupting apparatus which susbtantially eliminates arcing of the contacts upon opening or closing, and which interrupts the load current at the first current zero following the opening of the auxiliary contacts on the circuit interrupting device.

This substantially reduces maintenance and downtime due to deterioration of the contacts, allows the contacts to be made less expensively, and reduces deterioration of insulating dielectric in the event the contacts are disposed in such a dielectric. Further, the interrupting of the load current at the first current zero after the opening of the circuit interrupter, makes the disclosed apparatus particularly suitable for circuits requiring extremely fast switching, such as underload tap changing systems.

Since numerous changes may be made in the abovedescribed apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative, and not in a limiting sense.

I claim as my invention:

1. A circuit interrupting device comprising first and second contact means, means for opening and closing said first and second contact means, means for causing said first contact means to open prior to the opening of said second contact means, transformer means having a plurality of windings, said second contact means being connected in series circuit relation with one of said plurality of windings, said serially connected second contact means and winding being connected in parallel circuit relation with said first contact means, first and second controlled rectifiers each having main and control electrodes, means connecting the main electrodes of each of said first and second controlled rectifiers in separate parallel circuits around said series connected second contact means and winding, said first and second controlled rectifiers being poled in opposite directions, means connecting another of said plurality of windings in circuit relation with the control electrode of said first controlled rectifier, and means connecting another of said plurality of windings in circuit relation with the control electrode of said sec ond controlled rectifier, said windings applying signals of opposite polarity to the control electrodes of said first and second controlled rectifiers when current having a predetermined magnitude flows through said series connected second contact means and winding.

2. A circuit interrupting device comprising main and auxiliary contacts, means for opening and closing said main and auxiliary contacts and for causing said main contacts to open prior to the opening of said auxiliary contacts and close after the closing of said auxiliary contacts, transformer means having first, second and third windings, said auxiliary contacts being connected in series circuit relation with said first winding, said serially connected auxiliary contacts and first winding being connected in parallel circuit relation with said main contacts, first and second controlled rectifiers each having main and control electrodes, means connecting the main electrodes of said first and second controlled rectifiers in separate parallel circuits around said series connected auxiliary contacts and first winding, said first and second controlled rectifiers being poled in opposite directions, means connecting said second winding in circuit relation with the control electrode of said first controlled rectifier, and means connecting said third winding in circuit relation with the control electrode of said second controlled rectifier, said second and third windings applying signals of opposite polarity to the control electrode of said first and second controlled rectifiers when current flows through said series connected auxiliary contacts and first winding, to switch one of said controlled rectifiers to its cono u ductive state and shunt said main and auxiliary contacts, at least until the first current zero.

3. A circuit interrupting device comprising main and auxiliary contacts, means for opening and closing said main and auxiliary contacts and for causing said main contacts to open prior to the opening of said auxiliary contacts and close after the closing of said auxiliary contacts, transformer means having first, second and third windings, said auxiliary contacts being connected in series circuit relation with said first winding, said serially connected auxiliary contacts and first winding being connected in parallel circuit relation with said main contacts, first and second controlled rectifiers each having main and control electrodes, means connecting the main electrodes of each of said first and second controlled rectifiers in separate parallel circuits around said series connected auxiliary contacts and first winding, said first and second controlled rectifiers being poled in opposite directions, means connecting said second winding in circuit relation with the control electrode of said first controlled rectifier, voltage clipping means connected across said second winding, and means connecting said third winding in circuit relation with the control electrode of said second controlled rectifier, said second and third windings applying signals of opposite polarity to the control electrodes of said first and second controlled rectifiers when current fiows through said series connected auxiliary contacts and first winding, to switch one of said controlled rectifiers to its conductive state and shunt said main and auxiliary contacts, at least until the first current zero.

4. Protective apparatus for circuit interrupting devices which have parallel connected main and auxiliary contacts, with the auxiliary contacts being arranged to open after the main contacts have opened, comprising a transformer having first, second and third windings, said first winding being connected in series circuit relation with the auxiliary contacts, first and second controlled rectifiers each having main and control electrodes, means connecting the main electrodes of said first and second controlled rectifiers in separate parallel circuits around said series connected auxiliary contacts and first winding, said first and second controlled rectifiers being poled in opposite directions, means connecting said second Winding in circuit relation with the control electrode of said first controlled rectifier, and means connecting said third winding in circuit relation with the control electrode of said second controlled rectifier, said second and third windings applying signals of opposite polarity to the control electrodes of said first and second con-trolled rectifiers when current flows through said series connected auxiliary contacts and first winding.

5. Protective apparatus for circuit interrupting devices which have parallel connected main and auxiliary contacts, with the auxiliary contacts being arranged to open after the main contacts have opened, and close before the main contacts have closed, comprising a transformer having first, second and third windings, said first winding being connected in series circuit relation with the auxiliary contacts, first and second controlled rectifiers each having main and control electrodes, means connecting the main electrodes of said first and second controlled rec- .tifiers in separate parallel circuits around said series connected auxiliary contacts and first winding, said first and second controlled rectifiers being poled in opposite directions, means connecting said second winding in circuit relation with the control electrode of said first controlled rectifier, voltage clipping means connected across said second winding, and means connecting said third winding in circuit relation with the control electrode of said second controlled rectifier, said second and third windings applying signals of opposite polarity to the control electrodes of said first and second controlled rectifiers when current having a predetermined magnitude flows through said series connected auxiliary contacts and first winding.

6. A circuit interrupting device comprising main and auxiliary contacts, means for opening and closing said main and auxiliary contacts, means for causing said auxiliary contacts to close before the closing of said rnain contacts, to open once said rnain contacts have closed, and to close before said main contacts open to allow said main contacts to open prior to the opening of said auxiliary contacts, transformer means having first, second and third windings, said auxiliary contacts being connected in series circuit relation with said first Winding, said serially connected auxiliary contacts and first winding being connected in parallel circuit relation With said main contacts, first and second controlled rectifiers each having main and control electrodes, means connecting the main electrodes of said first and second controlled rectifiers in separate parallel circuits around said series connected auxiliary contacts and first winding, said first and second controlled rectifiers being poled in opposite directions, means connecting said second winding in circuit relation with the control electrode of said first controlled rectifier, and means connecting said third winding in circuit relation References tlited by the Examiner UNITED STATES PATENTS 2,157,925 5/ 1939 Stoddard.

2,215,804 9/ 1940 West.

2,665,396 1/ 1954 Weinfurt.

2,789,253 4/ 1957 Vang.

3,184,653 5/ 1965 Hutson 317-11 X STEPHEN W. CAPELLI, Primary Examiner.

SAMUEL BERNSTEIN, Examiner.

R. V. LUPO, Assistant Examiner. 

1. A CIRCUIT INTERRUPTING DEVICE COMPRISING FIRST AND SECOND CONTACT MEANS, MEANS FOR OPENING AND CLOSING SAID FIRST AND SECOND CONTACT MEANS, MEANS FOR CAUSING SAID FIRST CONTACT MEANS TO OPEN PRIOR TO THE OPENING OF SAID SECOND CONTACT MEANS, TRANSFORMER MEANS HAVING A PLURALITY OF WINDINGS, SAID SECOND CONTACT MEANS BEING CONNECTED IN SERIES CIRCUIT RELATION WITH ONE OF SAID PLURALITY OF WINDINGS, SAID SERIALLY CONNECTED SECOND CONTACT MEANS AND WINDING BEING CONNECTED IN PARALLEL CIRCUIT RELATION WITH SAID FIRST CONTACT MEANS, FIRST AND SECOND CONTROLLED RECTIFIERS EACH HAVING MAIN AND CONTROL ELECTRODES, MEANS CONNECTING THE MAIN ELECTRODES OF EACH OF SAID FIRST AND SECOND CONTROLLED RECTIFIERS IN SEPARATE PARALLEL CIRCUITS AROUND SAID SERIES CONNECTED SECOND CONTACT MEANS AND WINDING, SAID FIRST AND SECOND CONTROLLED RECTIFIERS BEING POLED IN OPPOSITE DIRECTIONS, MEANS CONNECTING ANOTHER OF SAID PLURALITY OF WINDINGS IN CIRCUIT RELATION WITH THE CONTROL ELECTRODE OF SAID FIRST CONTROLLED RECTIFIER, AND MEANS CONNECTING ANOTHER OF SAID PLURALITY OF WINDINGS IN CIRCUIT RELATION WITH THE CONTROL ELECTRODE OF SAID SECOND CONTROLLED RECTIFIER, SAID WINDINGS APPLYING SIGNALS OF OPPOSITELY POLARITY TO THE CONTROL ELECTRODES OF SAID FIRST AND SECOND CONTROLLED RECTIFIERS WHEN CURRENT HAVING A PREDETERMINED MAGNITUDE FLOWS THROUGH SAID SERIES CONNECTED SECOND CONTACT MEANS AND WINDING. 